Infant incubators are arranged so that the mattress upon which the infant lies can be tilted for certain medical procedures and conditions and lifted to permit placement of an X-ray cassette under the mattress tray without disturbing the baby. In some incubators, mattress tilt or lift is accomplished by simple lever mechanisms with positive stops at one or two positions. Such lever mechanisms are difficult to operate in a smooth manner because of the positive stops When the mattress nears the positive stop position, it can undergo a sudden, rapid, small displacement as the stopping mechanism locks in place. This movement can startle an infant on the mattress. Another disadvantage of such lever mechanisms is that the mattress can be positioned only at the preset stops.
Other infant incubators have somewhat complex mechanisms to provide a continuously variable mattress tilt or lift. Typically, these mechanisms employ long lead screws. Among the drawbacks of these mechanisms is that they are difficult to clean which must be done on a regular basis because they are located inside the incubator environment. The difficulty in cleaning comes about because of the extended length of the threaded profile of the lead screw and it is usually in an area that is difficult to access.
Another shortcoming of some lead screw mechanisms currently in use is that the mechanical advantage varies from one end of the stroke to the other end, whereby there is a large rise of the mattress for each crank revolution at one end of the stroke and a small rise for each crank revolution at the other end of the stroke. This results in a high torque requirement on the input crank at one end of the stroke or an inordinate number of turns required on the crank at the other end of the stroke or both.
Other shortcomings of incubator mattress lift arrangements in use at the present time which employ lead screw mechanisms are high cost and complicated linkage design.
U.S. Pat. No. 3,335,713 to Grosholz et al. discloses an infant incubator in which the inclination of the mattress support tray is controlled by a pneumatic cell. The arrangement disclosed in this patent, however, provides inadequate longitudinal and transverse stability to the mattress support tray when forces are applied to the mattress support tray when, for example, the infant on the mattress is being treated or equipment is placed on the mattress.